The present invention relates to a double acting drive mechanism capable of operating vehicle accessories at one of either two speed ratios or to totally disengage the accessories from a vehicle engine.
Present day automotive vehicles are typically provided with a number of belt driven engine accessories, such as an air pump, an alternator, a power steering pump and an air conditioning compressor. These accessories exert a parasitic drag on the vehicle engine which is especially evident during periods of vehicle acceleration as well as during periods of engine start-up. This parasitic drag may not be noticeable when considering the larger six or eight cylinder engines; however, it may become a significant factor and distract from engine performance of the smaller three and four cylinder engines now commonly in use.
Accordingly, it is an object of the invention to provide an accessory drive which conserves fuel and increases engine performance by permitting the engine driven accessories to be driven through either of two belt drives one of which provides a high speed of rotation while the other of which provides a lower speed of rotation. Appropriate sensors may be incorporated within the system to sense various engine operating conditions to determine when the lower speed of operation is desirable to cause the clutch to switch between the higher and low speed modes of operation. Further during engine start-up, especially during cold whether operation it may be desirable to momentarily disengage the accessories from the engine to permit same to start quickly in an environment removed from the parasitic drag of the accessories. Accordingly the present invention comprises a drive comprising a first and a second pulley rotationally isolated from an input shaft and adapted to be engagably connected to the input shaft. The drive further includes a plate rotatable with the input shaft and axially movable thereon between a first position in engagement with the first pulley and a second position in engagement with the second pulley; means supported by one of the pulleys for urging the plate to move into engagement with the other of the pulleys, including a rolling diaphragm attached to the one pulley defining an activation chamber therebetween, means for communicating pressurized fluid to the activation chamber; and means for biasing the plate toward and into engagement with the one pulley.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawing.